Many internal combustion engines generate power using cooperative engine cylinder and piston arrangements that define a variable volume chamber for combustion events. Alternatively, cylinder and rotor arrangements are used to harness energy from combustion events. The motion of the engine pistons or the rotors may be used to intake or scavenge an air-fuel mixture or strictly air charge (in fuel injected engines) for combustion and expel spent exhaust gases in multicycle operations, such as, for example, in 2-cycle and 4-cycle operations. There are many inefficiencies in both piston and rotor type internal combustion engines which it would be beneficial to decrease or eliminate. Such inefficiencies may result, at least in part, from the nature of the variable volume chamber used to generate power from combustion events.
For example, the pistons in a piston type engine must constantly accelerate, travel, deaccelerate, stop, and reverse their motion in the region of bottom dead center and top dead center positions to create a variable volume chamber. While this constantly reversing pumping motion of the piston produces a variable volume chamber formed between the piston head and the surrounding cylinder, it eliminates conservation of momentum, thereby reducing efficiency. Accordingly, there is a need for engines and methods of engine operation that use variable volume combustion chambers while preserving at least some of the momentum built up through repeated combustion events.
Rotary engines are known for their superior mechanical efficiency as compared with piston type engines due to the fluid, non-stop motion of the rotary engine elements that preserve momentum. However, engine efficiency and power may also be a function of the mass of air in the combustion chamber. The air mass that can be loaded into the combustion chamber is a function of the pressure differential between the combustion chamber and the intake air source (e.g., manifold) during the intake cycle, as well as the effective size and flow characteristics of the intake port, and the duration of the intake cycle event. Piston type engines take advantage of a variable volume combustion chamber to further increase the pressure of a combustion charge by decreasing the volume of the chamber once it is loaded with the charge. Increasing any one or more of the combustion charge pressure, the effective size and/or flow profile of the intake port, and/or the effective intake cycle duration, will tend to increase air mass in the combustion chamber, and thus improve efficiency and power. Rotary type engines are less able to compress a combustion charge as compared with a piston type engine, decreasing efficiency as a result. Accordingly, there is a need for engines and methods of engine operation that increase and/or improve combustion charge pressure, intake port size and flow, and/or intake event duration, while at the same time improving upon the preservation of engine momentum.
One method of increasing combustion charge pressure is to use a turbocharger or a supercharger to boost the pressure of intake air supplied for the combustion process. Existing turbochargers and superchargers add weight, cost, and complexity when they utilize add-on elements that are otherwise unneeded for engine operation. Accordingly, there is a need for engines and methods of engine operation that use combustion generating components to also supercharge the intake air supply, thereby eliminating or reducing the need for dedicated supercharging add-on components.
Rotary engines, such as a Wankel rotary engine, have other advantages over reciprocating piston engines, such as: fewer components resulting from elimination of the valve train; lower vibration due to the elimination of reciprocating mass; lower weight and size for the power output; and smoother power delivery into a higher RPM range. However, Wankel rotary engines are not optimal in terms of fuel economy due to lower combustion chamber compression ratios, or in terms of emissions due to the more complete and faster combustion in piston engines. Accordingly, there is a need for engines and methods of engine operation that provide one or more of the benefits of both rotor type and piston type engines at the same time.
Existing piston type and rotor type almost universally require liquid lubricant, such as engine oil, to lubricate the interface between the piston or rotor and the cylinder within which it moves. Lubrication systems are usually mission critical and the failure of a lubrication system can be catastrophic. The need for a lubricant brings with it many disadvantages. The lubricant wears out and becomes contaminated over time, and thus requires replacement, adding expense and inconvenience to engine operation. Many lubricants require pumps and passages to reapply the lubricant to moving parts. Pumps and passages, and other elements of an active lubrication system need to operate correctly and require seals between interconnected elements. Lubrication system leaks naturally occur as seals deteriorate over time, and pumps leak and wear out, adding still further maintenance expense and inconvenience to engine operation. Leaks can also permit lubricant to enter the combustion chamber, interfering with combustion, and fouling injectors and spark or glow plugs. Lubricant in the combustion chamber can also result in unwanted exhaust emissions. Leaks can also result in the contamination of the lubricant with combustion by-products. All of the foregoing issues are attendant to the use of lubricants, and all add failure modes and maintenance costs. Accordingly, there is a need for internal combustion engines and methods of engine operation that depend less, or not at all, on lubricants.
The ability to limit or eliminate the use of lubricants in an engine may be a function of the sealing area for the combustion chamber. A larger sealing area for a given pressure difference across the seal permits the use of less effective seals, or produces a stronger sealing action and longer seal life. A larger seal area may also eliminate or reduce the prevalence of chamber hot spots and heat transfer issues, and permit better utilization of the thermodynamic energy produced. Accordingly, there is a need for internal combustion engines and methods of engine operation that include larger seal areas for a given combustion chamber displacement.
Two additional factors which impact engine efficiency are flame front propagation during combustion of fuel, and effective force transfer from the expansion of combustion gases to the piston used to generate power. Improved flame front propagation may provide more complete combustion and thus enhance fuel economy. Improved force transfer from combustion expansion may also improve fuel economy. Accordingly, there is a need for engines with superior flame front propagation and force transfer from expanding combustion gasses to the power generating elements.
Internal combustion engines generate waste heat as a matter of course which is dumped into the ambient environment using one or more cooling systems such as radiators and exhaust systems. Waste heat is by definition not used to generate output power and thus represents a form of inefficiency. Accordingly, there is a need for internal combustion engines which utilize what would otherwise be waste heat to generate positive power.
Boosting the pressure of air in internal combustion engines may benefit efficiency in many respects. Superchargers provide one means for boosting air pressures, however, they add cost and weight, take up space, and require maintenance. Accordingly, there is a need for superchargers that are superior to existing superchargers in terms of cost, weight, space utilization, and maintenance requirements.
The variable volume chamber of a piston type internal combustion engine may be used in non-engine applications to provide a fluid pump or compressor. However, the efficiency of piston type pumps and compressors is reduced for many of the same reasons that the efficiency of piston type engines is sub-optimal. For example, the lack of preservation of piston momentum negatively affects the efficiency of piston type pumps and compressors. Accordingly, there is a need for pumps and compressors that avoid one or more of the disadvantages of known piston type pumps and compressors.